Abstract: A percussive tool, particularly a chisel for percussive working in rock, has a body portion, and a nozzle arrangement in the body portion, which is operative for forming a high-speed flow of a high-pressure fluid, particularly liquid, and directing the same to a working region of the body portion. The nozzle arrangement may include a plurality of nozzle holes which are open into the working region. It may also include at least one nozzle hole and at least one nozzle directing the flow of fluid into the nozzle hole. The nozzle may be supported by a supporting member which has an inner passage and extends from an inner chamber of a head section of the body portion into a receiving recess of a shaft section of the latter. The supporting member may be adjustable in the direction of a longitudinal axis of the chisel.

Abstract: An overpressure valve for a hydraulic pit prop comprises a housing, a valve seat provided in the housing, a valve body movable in axial direction in the housing between a closed position engaging the valve seat and an open position, and bellows means filled with a gas under pressure arranged for biasing the valve body to the closed position.